Process for producing a nonwoven polyester staple fiber fabric

ABSTRACT

Polyester staple fibers containing a polymeric blend of 0.5 to 15 mass % of a polyolefinic polymer with a matrix polyester polymer, 50% or more of the surface area of each fiber being formed by the polymeric blend, are useful for forming a nonwoven fabric with soft hand and a uniform texture by using various web-forming methods, for example, an air laid, wet laid or carding method.

CROSS REFERENCE TO RELATED APPLICATION

This is a Continuation application of U.S. application Ser. No.10/487,222 filed on Feb. 20, 2004, which is a 371 of PCT Application No.PCT/JP03/07754 filed on Jun. 18, 2003, which applications areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a polyester staple fiber and a nonwovenfabric comprising the same.

TECHNICAL BACKGROUND

Polyester staple fibers have excellent mechanical properties andresistances to chemicals, and therefore are widely employed for nonwovenfabrics. However, the nonwoven fabrics comprising conventional polyesterstaple fibers are disadvantageous in that the fabrics exhibit anundesirable creaky touch and an unsatisfactory soft hand, in comparisonwith nonwoven fabrics comprising nylon or polyolefin staple fibers.

It is known that the nonwoven fabrics can be produced from staple fibersby a method in which a web is formed from the staple fibers by a cardingmethod, a wet laid method or an air-laid method and then the staplefibers in the web are entangled with each other by a needle-punching ora spunlacing or hydro-entangling procedure, or are heat-bonded underpressure by a calender or embosser, or the web is impregnated with anemulsion of a binder and dried to chemically-bond the staple fibers inthe web with each other. In the case where, in the above-mentionedmethods, the web is formed by the air laid procedure, the polyesterstaple fibers are disadvantageous in that, in comparison with nylon orpolyolefin staple fibers, the smoothness of the polyester stable fibersis low and, when crimped, the resultant crimped fibers easily exhibit ahigh percentage of crimp, and thus a low fiber-opening property in theambient air atmosphere, and therefore, production of a nonwoven fabrichaving a uniform texture from the polyester staple fibers is difficult.This trend is significantly realized when undrawn polyester fibers orcopolymeric polyester fibers which have a low degree of orientation anda low degree of crystallinity and are preferred as binder fibers, areemployed for the production of the nonwoven fabrics. Therefore, there isa limit in the production of the nonwoven fabrics having a uniformtexture, from a web formed by using the binder fibers, particularly from100% of the binder fibers, by the air laid method. Also, even in thecase where the carding method or wet laid method is employed, aproduction of nonwoven fabrics having a uniform texture from thepolyester staple fibers having a low surface smoothness and thusexhibiting a poor fiber-opening property, is difficult.

The above-mentioned trend is further intensified when the web is formedfrom the binder fibers by a carding method.

The difficulty in the production of the nonwoven fabrics appears to becaused from a high rigidity of the polyester staple fibers and frictionbetween individual polyester staple fibers. To solve this problem,Japanese Examined Patent Publication No. 48-1480 discloses a method inwhich a dimethylsiloxane compound or a amine-modified silicone compoundis applied to surfaces of the polyester fibers and cross-linking theapplied compound by heating. However, in the case where the treatedpolyester staple fibers are formed into a web by, for example, a cardingmethod, the staple fibers of the Japanese publication have very littlefriction between the fibers and thus exhibit an insufficientfiber-entangling property and the resulting web is easily broken. Inthis case, when the web is formed by the wet laid method, as the staplefibers of the Japanese publication repel water, the fibers are notevenly dispersed in water. Also, while the web is formed by the air-laidmethod, static electricity is generated on the staple fibers of theJapanese publication and, in the resultant web, the staple fibers areunevenly distributed. Further, when the staple fibers of the Japanesepublication are used as binder fibers, the surface-treating agentapplied to the surfaces of the polyester staple fibers forms a barrieragainst the heat-bonding of the fibers.

SUMMARY OF THE INVENTION

The present invention was made to solve the problems of the prior arts.Namely, an object of the present invention is to provide polyesterstaple fibers enabling a nonwoven fabric having a soft hand and auniform texture to be realized, and a nonwoven fabric comprising thepolyester staple fibers. Further, the present invention is intended toprovide a nonwoven fabric produced from a web formed from the polyesterstaple fibers by an air laid method and having the above-mentionedexcellent quality.

The inventors of the present invention found that polyester staplefibers, portions of the peripheral surfaces of which are formed from apolymeric blend of a polyester and a polyolefin mixed and dispersed inthe polyester, exhibit appropriate friction between the staple fibers,and a nonwoven fabric having not only a soft hand, but also a veryuniform texture can be obtained in the case where the content of thepolyolefin in the fibers is established within a specific range of thecontent.

Namely, the above-mentioned object can be attained by the polyesterstaple fiber of the present invention comprising a polymeric blendcomprising 0.5 to 15% by mass of a polyolefinic polymer mixed anddispersed in a matrix polyester polymer, 50% or more of the surface areaof the fiber being formed by the polymeric blend.

In the polyester staple fiber of the present invention, the polyolefinicpolymer preferably comprises at least one member selected frompolyethylene, polypropylene, ethylene-propylene copolymers andpolyethylene copolymers and polypropylene copolymers in which at leastone ethylenically unsaturated monomer different from ethylene andpropylene is block-copolymerized or graft-copolymerized.

In the polyester staple fiber of the present invention, the matrixpolyester polymer is preferably selected from polyalkyleneterephthalates and polyalkylene terephthalate-isophthalate copolymers.

The polyester staple fiber of the present invention preferably has adegree of crystallization of 20% or less or a birefringence of 0.05 orless.

The polyester staple fiber of the present invention preferably has aconcentric or eccentric core-in-sheath conjugate structure in which thesheath section is formed from the polymeric blend.

The polyester staple fiber of the present invention preferably has afiber length of 2 to 30 mm, and a plane zigzag type or omega (ω) typecrimps in the number of crimps of 3 to 13 crimps/25 mm and a percentageof crimp of 3 to 15%.

The polyester staple fiber of the present invention preferably has afiber length of 30 to 200 mm, and a number of crimps of 5 to 30crimps/25 mm and a percentage of crimps of 3 to 30%.

The nonwoven fabric (1) of the present invention comprises a pluralityof the polyester staple fibers as mentioned above, and formed by an airlaid web-forming method.

The nonwoven fabric (1) of the present invention preferably has apercentage of non-opened fibers of 5% or less.

The nonwoven fabric (2) of the present invention comprises a pluralityof the polyester staple fibers as mentioned above, and is formed by awet laid web-forming method.

The nonwoven fabric (3) of the present invention comprises a pluralityof the polyester staple fibers as mentioned above and is formed by acarding web-forming method.

The nonwoven fabric (1), (2) or (3) of the present invention preferablyhas a bending resistance of 70 mm or less, determined by the cantilevermethod.

BEST MODE CARRYING OUT THE INVENTION

The staple fibers of the present invention are polyester staple fibers50% the surface area of which are formed by a polymeric blend comprisinga polyolefinic polymer mixed and dispersed in a matrix polyesterpolymer.

The polyester polymers usable for the present invention include, forexample, polyesters of aromatic dicarboxylic acids with aliphatic diols,such as polyalkylene terephthalates, for example, polyethyleneterephthalate, polytrimethylene terephthalate and polybutyleneterephthalate and polyalkylene naphthalates, for example, polyethylenenaphthalates; polyesters of cycloaliphalic dicarboxylic acids withaliphatic diols, for example, polyalkylene cyclohexane-dicarboxylates;polyesters of aromatic dicarboxylic acids with cycloaliphatic diols, forexample, polycyclohexanedimethanol terephthalate; polyesters ofaliphatic dicarboxylic acids with aliphatic diols, for example,polyethylene succinate, polybutylene succinate, polyethylene adipate andpolybutylene adipate; and polyhydroxycarboxylate esters, for example,polylactate esters and polyhydroxybenzoate esters. The polyesters usablefor the present invention may be copolyesters containing at least onecopolymerizing component selected from acid components, for example,isophthalic acid, phthalic acid, adipic acid, sebacic acid,α,β-(4-carboxyphenoxy)ethane, 4,4-dicarboxyphenyl, 5-sodiumsulfoisophthatic acid, 2,6-naphthalene dicarboxylic acid and1,4-cyclohexanedicarboxylic acid and esters of the above-mentionedacids, and diol components, for example, diethylene glycol,1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol,1,4-cyclohexane dimethanol and polyalkylene glycol. The copolymerizingcomponent may be selected from compounds having three or more carboxylicacid groups or hydroxyl groups, for example, pentaerythritol,trimethylolpropane, trimellitic acid, and trimesic acid, to cause theresultant copolyesters have branched chains. In the present invention,the above-mentioned polyester polymers (copolymers) may be employedalone or in a mixture of two or more thereof.

The polyester polymer and the polyolefinic polymer may contain one ormore of additives, fluorescent brightening agents, stabilizers, flameretardants, flame retardant assistants, ultraviolet ray absorbers,anti-oxidants and various coloring pigments, as long as the effects ofthe present invention are not degraded.

In the polymeric blend for the polyester staple fibers of the presentinvention, the content of the polyolefinic polymer to be mixed anddispersed in the matrix polyester polymer must be in the range of from0.5 to 15% by mass, preferably from 1 to 10% by mass, more preferably 2to 7% by mass, still more preferably 2 to 5% by mass, based on the massof the polymeric blend. If the content of the polyolefinic polymer isless than 0.5% by mass, the object of the present invention, namely apreparation of the polyester staple fiber-containing nonwoven fabrichaving the soft hand and the uniform texture cannot be attained. Also,if the polyolefinic polymer content is more than 15% by mass, not onlythe above-mentioned effect is saturated or cannot be obtained, but alsothe fiber-forming property of the resultant polymeric blend is degradedand thus the target staple fibers of the present invention cannot beproduced.

In the polyester staple fibers of the present invention, 50% or more,preferably 70% or more, more preferably 90% to 100%, of the surfaceareas of the fibers must be formed from the polymeric blend. If theproportion of the surface area formed by the polymeric blend is lessthan 50%, the resultant nonwoven fabric exhibits an insufficientsoftness and an unsatisfactory uniformity in texture. The staple fiberssatisfying the above-mentioned requirement include staple fibers formedfrom 100% by mass of the polymeric blend and conjugate staple fibers inwhich the polymeric blend forms 50% or more of the surface areas of thefibers. The conjugate staple fibers include concentric core-in-sheathtype, eccentric core-in-sheath type, side-by-side type andislands-in-sea type and segment pie type conjugate staple fibers.Preferably, the concentric and eccentric core-in-sheath conjugate staplefibers in which 70% or more, more preferably 100% of the fiber surfacearea is formed by the polymeric blend sheath section, are employed forthe present invention.

The polyester staple fibers of the present invention may be hollowfibers or non-hollow fibers. The cross-sectional profile of thepolyester staple fibers of the present invention is not limited tocircular and may be selected from irregular profiles, for example, oval,multi-lobed, for example, three to eight lobed and polygonal such as, asexamples, triangle to octagonal profiles.

The effect of the present invention is significantly realized in thepolyester staple fibers having a birefringence of 0.05 or less or adegree of crystallinity of 20% or less.

In the conventional polyester staple fibers having a birefringence of0.05 or less or a degree of crystallinity of 20% or less, there is atrend to increase the friction between the fibers, and thus theresultant nonwoven fabric may exhibit a degraded hand, reducedfiber-opening property and, thus, an unsatisfactory uniformity intexture of the fibers. This trend appears to be significant in the loworientation fibers (undrawn fibers) produced by melt-spinning apolyalkylene terephthalate, particularly, a isophthalicacid-copolymerized polyalkylene terephtalate, at a low taking-up speedof 2000 m/minute or less. Among the undrawn polyalkylene terephthalatefibers, the above-mentioned trend appears to be very significant in thefibers formed from the polyethylene terephthalate having a low degree ofcrystallinity and the copolymerized polyethylene terephthalate with 5 to50 molar % of isophthalic acid based on the total molar amount of theacid component. The above-mentioned polyester staple fibers can beheat-bonded under pressure to each other and are usable as binder fibersfor the nonwoven fabric. When the above-mentioned polyester polymer isused as a matrix polymer of the polyester staple fibers of the presentinvention, the resultant polyester staple fibers can be used as binderfibers without causing the above-mentioned problem. Also, the resultantpolyester staple fibers of the present invention are useful for theproduction of the nonwoven fabric having a desired soft hand and uniformtexture.

There is no limitation to the thickness of the individual polyesterstaple fibers of the present invention. Usually, the thickness of thepolyester staple fibers of the present invention is preferably in therange of 0.01 to 500 dtex.

The polyester staple fibers of the present invention can be produced by,for example, the process illustrated below. A melt of a polymeric blendof a polyester polymer with a polyolefinic polymer is extruded through a(melt-)spinneret having a plurality of spinning orifice of aconventional (melt-)spinning apparatus, the extruded filamentary streamsof the melt are cooled and solidified by blowing cooling air toward themelt streams and drafting, the solidified filaments are taken-up at aspeed of 100 to 2000 m/minute to provide undrawn polyestermulti-filament yarn.

The melt of the polymeric blend is prepared by blending a melt of thepolyester polymer with a melt of the polyolefinic polymer by a staticmixer, or dynamic mixer or by blending pellets of the polyester polymerand the polyolefinic polymer with each other in a desired mass ratio and(melt-)kneading the blend by using a (melt-)extruder, and the resultantblend melt is fed to the (melt-)spinneret.

In the production of the undrawn polyester conjugate filaments, the sameprocedures as mentioned above are carried out, except that a melt of thepolymeric blend and a melt of a polyester resin are separately fed intoa (melt-)spinneret in which the melts of the polymeric blend and thepolyester resin are combined so as to form conjugate filaments of eachof which, 50% or more of the surface area are formed by the polymericblend.

The resultant undrawn filaments are drawn at a desired draw ratio in hotwater at a temperature of 70 to 100° C. or in steam at a temperature of100 to 125° C., and optionally the resultant drawn filaments arecrimped, oiled with a finish oil in consideration of the use and theobject of the resultant staple fibers, dried and relaxed. The resultantfilaments are cut into staple fibers having a desired fiber length, toobtain the target polyester staple fibers. In the procedures, the oilingagent may contain a silicone compound of the type and in the amountwhich do not hinder the attainment of the object of the presentinvention. Also, the polyester staple fibers of the present inventionhaving a birefringence of 0.05 or less or a degree of crystallinity of20% or less can be obtained by the same procedures as mentioned above,except that the drawing procedure is omitted and the finish oil isapplied to the undrawn filaments and the oiled undrawn filaments aredried at the temperature for the time which do not cause the degree ofcrystallinity of the dried filaments to exceed 20%. In the production ofthe nonwoven fabric from the polyester staple fibers of the presentinvention, preferably, the staple fiber length is adjusted and thecrimps are imparted in response to the method of forming a web from thefibers, as follows.

For example, in the case where the web is formed by an air laid method,the staple fiber length is preferably adjusted to 2 to 30 mm, morepreferably 3 to 20 mm. By adjusting the fiber length to not less than 2mm the desired staple fibers can be industrially produced at asatisfactory process stability, and by controlling the fiber length tonot more than 30 mm, the resultant staple fibers exhibit an enhancedfiber-opening property, and a high resistance to the generation of fiberlumps. The polyester staple fibers may be crimped fibers or may notcrimped fibers, in view of the use of the resultant nonwoven fabric.Namely, where the target nonwoven fabric must have a high bulkiness, thestaple fibers are preferably crimped fibers, and where the targetnonwoven fabric must have an enhanced fiber-opening property uponjetting air and an improved property of being uniformly scattered by airjet, no crimps may be imparted to the staple fibers. Where the crimpedstaple fibers are used in the web-forming air laid method, preferablythe number of crimps is 3 to 13 crimps/25 mm and the percentage ofcrimps is 3 to 15%. When the number of crimp is adjusted to not morethan 13 crimps/25 mm, and the percentage of crimps is regulated to notmore than 15%, the resultant nonwoven fabric may exhibit a satisfactoryfiber-opening property by air-blowing. As the polyester staple fibers ofthe present invention easily have a low number of crimps and percentageof crimps in comparison with those of the conventional polyester staplefibers, the adjustment of the number and percentage of crimps within theabove-mentioned range is easy. Also, to impart an appropriate bulkinessto the polyester staple fibers of the present invention, preferably, thenumber and percentage of crimps are adjusted to not less than 3crimps/25 mm and not less than 3% respectively. The mode of crimping ispreferably in a plane zigzag or ω (omega) form which are formed within aplane, rather than a three dimensional spiral crimping mode, because theplane zigzag or ω crimped staple fibers exhibit a higher fiber-openingproperty than the spirally crimped staple fiber.

By adjusting the number and percentage of crimps as mentioned above, thecontent of non-opened staple fibers in the resultant web by the air laidmethod can be reduced to 5% by mass or less.

In the case where the web for the nonwoven fabric is produced by a wetlaid web-forming method, due the above-mentioned reasons, the fiberlength of the polyester staple fibers is preferably 2 to 30 mm, morepreferably 3 to 20 mm. The staple fibers may be crimped or not crimped.Namely, the crimps are imparted in consideration of the use and purposeof the target nonwoven fabric, to the staple fibers. However, in view ofthe uniformity in distribution of the staple fibers dispersed in anaqueous slurry of the staple fibers for the wet laid web-formingprocedure, no crimped staple fibers are preferred for the wet laidweb-forming method.

In the case where the web for the target nonwoven fabric is formed by acarding web-forming method, the length of the polyester staple fibers ispreferably adjusted to 30 to 200 mm, more preferably 35 to 150 mm, stillmore preferably 40 to 100 mm. The fiber length not exceeding 30 mm mayenable the breakages of the resultant web due to insufficiententanglement of the staple fibers with each other to be prevented orreduced. Also, a fiber length not exceeding 200 mm may enable theopening property of the resultant staple fibers on the carding machineto be enhanced and the uniformity in texture of the resultant web to beimproved.

To improve the passing property of the staple fibers through the cardingmachine, the crimped polyester staple fibers are preferably employed.The preferable number and percentage of crimps to be imparted to thepolyester staple fibers are 5 to 30 crimps/25 mm and 3 to 30%,respectively. The number and percentage of crimps adjusted not more than30 crimps/25 mm and not more than 30% may enable the resultant polyesterstaple fibers exhibit a good opening property on the carding machine andthe resultant web to exhibit a satisfactory uniformity in texture. Also,the number and percentage of crimps adjusted to not less than 5crimps/25 mm and not less than 3% may enable the breakages of theresultant web due to the insufficient entanglement of the staple fiberswith each other to be prevented or reduced. The mode of crimping may beconventional plane zigzag or a ω (omega) mode or three dimensionalspiral node.

The nonwoven fabric comprising the polyester staple fibers of thepresent invention has a soft touch and good hand and can exhibit aresistance to bending, which represents a softness of the fabric, of 70mm or less, determined by the cantilever method.

The nonwoven fabric of the present invention includes nonwoven fabricscomprising the polyester staple fibers of the present invention mixedwith staple fibers other than the polyester staple fibers of the presentinvention and nonwoven fabric laminate comprising at least one nonwovenfabric layer comprising the polyester staple fibers of the presentinvention and at least one additional nonwoven fabric layer comprisingstaple fibers other than those of the present invention, laminated oneach other.

Particularly, the nonwoven fabric formed from the polyester staplefibers of the present invention alone exhibits a specific soft handother than that of the nonwoven fabric comprising the conventionalpolyester staple fibers, and thus is preferred in various uses.

In the polyester staple fibers of the present invention, 50% or more ofthe peripheral surface area of individual staple fibers are formed fromthe specific polymeric blend of a polyester polymer with 0.5 to 15% bymass of a polyolefinic polymer. This feature of the present inventionenables the resultant staple fibers to exhibit a reduced frictionbetween the fibers and thus an enhanced fiber-opening property andtherefore, the resultant nonwoven fabric to exhibit a soft hand and ahigh uniformity in texture thereof.

The mechanism of realizing the effects of the polyester staple fibersand the nonwoven fabric of the present invention has not yet becompletely clear. However, it is assumed that in the polymeric blendusable for the present invention, the polyolefinic polymer isincompatible with the polyester polymer and thus when an appropriateamount of the polyolefinic polymer is mixed and dispersed in a matrixconsisting of the polyester polymer, the polyolefinic polymer issuspended in the form of a plurality of islands located in a seaconsisting of the matrix polyester polymer, and when individual fibersare formed by using the polymeric blend, a portion of the islandsappears on at least a portion of the peripheral surface of each of theindividual fibers so as to roughen the peripheral surface, and thus theresultant individual fibers are mainly contacted with each other at theconvexed portions of the peripheral surfaces of the fibers and exhibit alow frictional coefficient with each other.

EXAMPLES

The present invention will be further illustrated by the followingexamples.

In the examples and comparative examples, the resultant staple fibersand nonwoven fabrics were tested in the items and by the measurementmethods as shown below.

(a) Fiber Thickness

The thickness of fibers was determined in accordance with JIS L1015-1992, 7.5.1, Method A.

(b) Fiber Length

The length of staple fibers was determined in accordance with JIS L1015-1992, 7.4.1, Direct Method (method C).

(c) The Number of Crimps and Percentage of Crimps

The number and percentage of crimps of crimped staple fibers weredetermined in accordance with JIS L 1015-1992, 7.12.

(d) Intrinsic Viscosity of Polyester Polymer

The intrinsic viscosity ([η]) of polyester polymer was measured inorthochlorophenol at a temperature of 35° C.

(e) Melt Index (MFR) of Polyester Polymer or Polyolefinic Polymer

The MFR of polyester polymer on polyolefinic polymer was measured inaccordance with JIS K 7210, under condition 4.

(f) Glass Transition Temperature (Tg) and Melting Temperature (Tm) ofPolyester Polymer or Polyolefinic Polymer

The glass transition temperature (Tg) and melting temperature (Tm) ofpolyester polymer or polyolefinic polymer was measured by using adifferential scanning calorimeter (model: DSC-7, made by Parkin-ElmerCo.) at a temperature-increasing rate of 20° C./minute.

(g) Degree of Crystallinity of Fibers

The degree of crystallinity of fibers was determined by measuring adensity ρ in g/cm³ of a fiber using a density-gradient tube containing amixture of n-heptane with carbon tetrachloride at a temperature of 25°C., and calculating it from the resultant density ρ of the fiber inaccordance with the following equation.xc=ρc(ρ−ρa)/ρ(ρc−ρa)wherein xc represents a degree of crystallinity, in % by mass, of thefibers, ρc represents a crystal density of polyethylene terephthalate,namely 1.455 g/cm³, pa represents an amorphous density of polyethyleneterephthalate, namely 1.335 g/cm³, and p represents the density of thefibers.

(h) Birefringence (Δn) of Fibers

The birefringence (Δn) of fibers was determined by a retardation methodusing, as an immersion liquid, bromonaphthalene and a Belec compensator,as disclosed in W. E. Morton and J. W. S. Hearle, “Physical Propertiesof Textile Fibers”, page 524 to 532, 22.2.1 Refractive Index andbirefringence to 22.2.3 Measurement of birefringence, published by theTextile Institute Butter Worths, Manchester & London.

(i) Percentage (u) of Non-Opened Fibers

Non-opened fiber lumps were taken-up from 10 g of a web produced by theair laid method, the mass (x) of the taken-up fiber lumps was measured,and the percentage (u) of the non-opened fibers in the web wascalculated in accordance with the following equation.u(%)=x/10×100wherein x represents a mass of the non-opened fiber lumps taken-up fromthe web and u represents a percentage of the non-opened fibers in theweb.

(j) Resistance of Non-Woven Fabric to Bending

The bending resistance of the nonwoven fabric was measured in accordancewith JIS L 1085-1992, 5.7. Method A (45° cantilever method). The lowerthe number, the higher the softness of the fabric.

(k) Evaluation of Woven Fabric Texture

The appearance of the woven fabric was observed by the naked eye andevaluated in the following three classes. Class Fabric texture 3 Nonon-opened fiber lump is found. No unevenness in mass distribution isfound. Texture of fabric is uniform. 2 Non-opened fiber lumps appear tobe not significant. Uneven mass distribution is found by naked eyeobservation. 1 Non-opened fiber lumps are significant. Uneven massdistribution is significant. The fabric texture is not uniform.

Example 1

Polyethylene terephthalate (PET) pellets dried under vacuum at 120° C.for 16 hours and having an intrinsic viscosity [η] of 0.61 and a meltingtemperature (Tm) of 256° C. and high density polyethylene (HDPE) pelletshaving a melt index (MFR) of 20 g/10 minuets and a melting temperature(Tm) of 131° C. were mixed with each other in a mass ratio of 97:3. Themixture was melted in a twin-screw extruder and the resultant melthaving a temperature of 280° C. was extruded through a (melt)-spinnerethaving 600 spinning round orifices having an inner diameter of 0.3 mm atan extruding rate of 200 g/minute. The extruded filamentary melt streamswere cooled with cooling air at a temperature of 30° C. and the cooledand solidified undrawn multifilament yarn was wound up at a speed of1150 m/minute. The undrawn multifilament yarn was subjected to acrimping procedure using a stuffing box type crimper, to impart planezigzag-formed crimps with the number of crimps of 8 crimps/25 mm and apercentage of crimps of 4% to the undrawn individual filaments of themultifilament yarn. The crimped multifilament yarn was oiled with 0.25%by dry mass, based on the dry mass of the yarn, of an oiling agentcomprising an alkylphosphate potassium salt and apolyoxyethylene-modified silicone in a mass ratio of 80/20, and dried byblowing hot air at a temperature of 45° C. The dried undrawnmultifilaments were cut into a fiber length of 5 mm. The resultantpolyester staple fibers had a thickness of 3.1 dtex, a degree ofcrystallinity of 16% and a birefringence of 0.0035.

The staple fibers were subjected to an air laid web-forming procedure toprovide a web having a basis mass of 50 g/m². The web was subjected to acalendering procedure using a pair of flat calender rollers having aroller surface temperature of 200° C. under a linear pressure of 80kPa·m at a speed of 20 m/minute, to prepare an air laid nonwoven,fabric. The nonwoven fabric had a bending resistance of 50 mm, apercentage (u) of non-opened fibers of 0.5% and a texture of thenonwoven fabric in class 3.

Example 2

Polyester staple fibers and an air laid nonwoven fabric were produced bythe same procedures as in Example 1, except that the PET was replaced bya polyethylene terephthalate isophthalate copolymer containing 10 molar% of copolyesterified isophthalic acid and having a melting temperatureof 220° C. The resultant polyester staple fibers had a thickness of 3.4dtex, a degree of crystallinity of 9%, and a birefringence of 0.0027.The resultant nonwoven fabric had a bending resistance of 44 mm, apercentage (u) of non-opened fibers of 0.8% and a nonwoven fabrictexture in class 3.

Example 3

Pellets of an amorphous polyethylene terephthalate isophthalatecopolymer containing 40 molar % of copolymerized isophthalic acid driedunder vacuum at 50° C. for 24 hours and having an intrinsic viscosity[η] of 0.55 and a glass transition temperature (Tg) of 65° C. andpellets of a high density polyethylene (HDPE) having a melt index (MFR)of 20 g/10 minuets and a melting temperature (Tm) of 131° C. were mixedwith each other in a mass ratio of 95:5. The mixture was melted in atwin-screw extruder to prepare a polymeric blend melt having atemperature of 250° C. Separately, pellets of a PET dried at atemperature of 120° C. for 16 hours and having an intrinsic viscosity[η] of 0.61 were melted in an extruder to prepare a PET melt having atemperature of 280° C.

The polymeric blend melt and the PET melt were subjected to a meltspinning procedure using a concentric core-in-sheath type conjugatefilament-forming spinneret having 1032 spinning orifices having an innerdiameter of 0.3 mm for forming core-in-sheath type composite filamentshaving sheath portions formed from the polymeric blend melt and a coreportions formed from the PET melt in a cross sectional area ratio (A/B)of the sheath portions (A) to the core portions (B) of 50:50.

The core-in-sheath type conjugate streams of the polymeric blend meltand the PET melt were extruded through the spinneret at a spinnerettemperature of 285° C. at a extruding rate of 870 g/minute, and cooledby blowing cooling air at a temperature of 30° C. The resultant undrawncore-in-sheath type conjugate multifilament yarn was wound up at a speedof 1150 m/minute. The undrawn conjugate multi filament yarn was drawn inhot water at a temperature of 80° C. at a draw ratio of 3.75, then thedrawn conjugate multifilament yarn was passed through a water bath at atemperature of 30° C. to cool the yarn and to prevent the fuse adhesionof the drawn individual filaments to each other, the cooled yarn wasoiled with 0.2% by dry mass of an oiling agent comprising analkylphosphate potassium salt and a polyoxyethylene-modified silicone ina mixing dry mass ratio of 80:20. The oiled yarn was crimped in astuffing box type crimper to impart plane zigzag-formed crimps in thenumber of crimps of 9 crimps/25 mm and a percentage of crimps of 12%, tothe individual conjugate filaments. The crimped filaments were dried ata temperature of 50° C. and cut into a fiber length of 5 mm. Theresultant staple conjugate fibers had a thickness of 2.1 dtex.

The staple conjugate fibers were subjected to an air laid web-formingprocedure to provide a web having a basis mass of 50 g/m². The web wassubjected to a heat-bonding procedure using a hot air blow at atemperature of 150° C. for 2 minutes to cause the individual stapleconjugate fibers to adhere at portions thereof crossing each other. Theresultant air laid nonwoven fabric had a bending resistance of 53 mm, apercentage of non-opened fibers of 0.7% and a texture of the nonwovenfabric in class 3.

Comparative Example 1

Polyester staple composite fibers and an air laid nonwoven fabric wereproduced by the same procedures as in Example 3, except that thepolymeric blend of the amorphous PET copolymer with HDPE for the sheathportions of the conjugate fibers was replaced by an amorphouspolyethylene terephthalate isophthalate copolymer containing 40 molar %of copolymerized isophthalic acid and having an intrinsic viscosity [η]of 0.55 and Tg of 65° C. The resultant staple conjugate fibers had athickness of 2.1 dtex. The resultant nonwoven fabric had a bendingresistance of 83 mm, a percentage of non-opened fibers of 11% and anonwoven fabric texture in class 1.

Comparative Example 2

A polymeric blend for the sheath portions of the core-in-sheath typeconjugate filaments was prepared by the same manner in Example 3, exceptthat a mixing ratio of the amorphous PET copolymer pellets to the HDPEwas changed from 95:5 to 84:16. The resultant polymeric blend exhibiteda poor filament-forming property and thus the melt-spinning procedurescould not be carried out.

Example 4

Polyester staple fibers and a nonwoven fabric were produced by the sameprocedures as in Example 3, with the following exceptions. In thepolymeric blend for the sheath portions of the conjugate filaments, theHDPE was replaced by an isotactic polypropylene resin having an MFR of30 g/10 minutes and a Tm of 160° C.

The resultant staple conjugate fibers had a thickness of 2.2 dtex. Theresultant nonwoven fabric had a bending strength of 58 mm, a percentageof non-opened fibers of 1.3% and a nonwoven fabric texture in class 3.

Example 5

Polyester staple fibers and a nonwoven fabric were produced by the sameprocedures as in Example 3, with the following exceptions.

In the polymeric blend for the sheath portions of the conjugatefilaments, the HDPE was replaced by an ethylenepropylene randomcopolymers in a copolymerization molar ratio of ethylene to propylene of37:63 and having an MFR of 50 g/10 minutes and a Tm of 135° C.

The resultant staple conjugate fibers had a thickness of 2.2 dtex.

The resultant nonwoven fabric had a bending resistance of 58 mm, apercentage of non-opened fibers of 1.3% and a nonwoven fabric texture inclass 3.

Example 6

Polyester staple fibers and a nonwoven fabric were produced by the sameprocedures as in Example 3, with the following exceptions.

In the polymeric blend for the sheath portions of the conjugatefilaments, the HDPE was replaced by a straight linear low densitypolyethylene graft-copolymerized with 3.5% by mass of maleic anhydrideand having an MFR of 8 g/10 minutes and a Tm of 96° C.

The resultant staple conjugate fibers had a thickness of 2.2 dtex.

The resultant nonwoven fabric had a bending resistance of 52 mm, apercentage of non-opened fibers of 0.8% and a nonwoven fabric texture inclass 3.

Example 7

Polyester staple fibers and a nonwoven fabric were produced by the sameprocedures as in Example 3, with the following exceptions.

The PET for the core portions of the conjugate filaments was replaced bynylon 6 having an intrinsic viscosity of 1.34, determined in metacresolat a temperature of 35° C. and a Tm of 215°c. Chips of the nylon 6 weremelted in an extruder to prepare a nylon 6 melt having a temperature of240° C. The melt-spinning for the core-in-sheath type conjugatefilaments was carried out at a spinneret temperature of 250° C. at anextruding rate of 500 g/minute. The resultant undrawn multifilament yarnwas drawn at a draw ratio of 2.1 at room temperature and then at a drawratio of 1.05 in hot water having a temperature of 55° C. The drawnmultifilament yarn was passed through a water bath to cool it and thenoiled in the same manner as in Example 3. The oiled multifilament yarnwas crimped with plane zigzag-formed crimps in the number of crimps of12 crimps/25 mm and in a percentage of crimps of 6.5% and then dried ata temperature of 45° C. The crimped multifilaments were cut into staplefibers in the same manner as in Example 3.

The resultant staple conjugate fibers had a thickness of 2.2 dtex.

The resultant nonwoven fabric had a bending resistance of 57 mm, apercentage of non-opened fibers of 1.6% and a nonwoven fabric texture inclass 3.

Example 8

Polyester staple fibers and a nonwoven fabric were produced by the sameprocedures as in Example 3, except that the staple fiber length waschanged from 5 mm to 3 mm.

The resultant nonwoven fabric had a bending resistance of 57 mm, apercentage of non-opened fibers of 1.6% and a nonwoven fabric texture inclass 3.

Example 9

Polyester staple fibers and a nonwoven fabric were produced by the sameprocedures as in Example 3, except that the concentric core-in-sheathtype conjugate filament-forming spinneret was replaced by an eccentriccore-in-sheath type conjugate filament-forming spinneret, the percentageof the crimps on the crimped fibers was changed from 12% to 15%, and thecrimps had an omega (w) form.

The resultant staple conjugate fibers had a thickness of 2.3 dtex.

The resultant nonwoven fabric had a bending resistance of 55 mm, apercentage of non-opened fibers of 0.9% and a nonwoven fabric texture inclass 3.

Example 10

Polyester staple fibers and a nonwoven fabric were produced by the sameprocedures as in Example 3, except that no crimping was applied to thedrawn composite multifilament yarn.

The resultant nonwoven fabric had a bending resistance of 53 mm, apercentage of non-opened fibers of 0.2% and a nonwoven fabric texture inclass 3.

Example 11

Polyester staple fibers prepared by the same procedures as in Example 10and wood pulp fibers in a mass ratio of 80:20 were suspended in water,while fully stirring, and a sheet having dimensions of about 25 cm×about25 cm and a dry basis mass of 50 g/m² was prepared from the aqueousmixed fiber slurry by using a square-shaped sheet-forming machine. Thesheet was dried at room temperature over 24 hours or more, then placedon a perforated polytetrafluoroethylene sheet and subjected to ashrinking treatment in a hot air-circulation type dryer at a temperatureof 120° C. for 5 minutes, to produce a wet laid method nonwoven fabric.

The resultant nonwoven fabric had a bending resistance of 38 mm and anonwoven fabric texture in class 3.

Comparative Example 3

Polyester staple fibers and a wet laid method nonwoven fabric wereproduced by the same procedures as in Example 11, except that thecrimping procedure for the drawn multifilament yarn was omitted.

The resultant nonwoven fabric had a bending resistance of 38 mm and anonwoven fabric texture in class 2.

Example 12

Polyester staple fibers were produced by the same procedures as inExample 3, except that fiber length of the staple fibers was changedfrom 5 mm to 51 mm.

The staple fibers were fed to a carding procedure using a roller cardingmachine to prepare a card web. In the carding procedure, the staplefibers exhibited a good carding machine-passing property. A plurality ofcard webs were superposed on each other to prepare a laminated webhaving a basis mass of 50 g/m².

The laminated web was subjected to the same heat-bonding procedure as inExample 3 using hot air streams to heat-bonding the staple fibers atcrossing portions thereof to each other. A carding method heat-bondingnonwoven fabric.

The resultant nonwoven fabric had a bending resistance of 58 mm and anonwoven fabric texture in class 3.

Example 13

Polyester staple fibers were produced by the same procedures as inExample 10, except that fiber length of the staple fibers was changedfrom 5 mm to 51 mm.

The staple fibers were fed to the same carding procedure as in Example12 to prepare a card web. In the carding procedure, the staple fibersexhibited a good carding machine-passing property. A plurality of cardwebs were superposed and heat-bonding in the same manner as in Example12 to produce a card method heat-bonding nonwoven fabric.

The resultant nonwoven fabric had a bending resistance of 51 mm and anonwoven fabric texture in class 3.

The present invention can provide specific polyester staple fibersuseful for forming a nonwoven fabric having a soft hand and a uniformtexture. Also, the present invention can provide a nonwoven fabrichaving not only a uniform texture but also a soft hand. Especially, thenonwoven fabric produced from a web formed from the polyester staplefibers of the present invention by an air laid web-forming method has avery low percentage of non-opened fibers and an excellent uniformity oftexture.

Accordingly, the specific polyester staple fibers enable the resultantnonwoven fabric produced from the staple fibers to have widened varioususes and thus have a high industrial value.

1-12. (canceled)
 13. A process for producing a nonwoven polyester staplefiber fabric comprising; preparing polyester staple fibers comprising apolymeric blend comprising 85 to 95.5% by mass of matrix polyesterpolymer and 0.5 to 15% by mass of a polyolefinic polymer mixed with anddispersed in the matrix polyester polymer, at least the surface of eachfiber being formed by the polymeric blend; and forming the polymericblend staple fibers into a nonwoven fabric by an air-laid web-formingmethod.
 14. The process for producing a nonwoven polyester staple fiberfabric as claimed in claim 13, wherein the polyolefinic polymercomprises at least one member selected from polyethylene, polypropylene,ethylene-propylene copolymers and polyethylene copolymers andpolypropylene copolymers in which at least one ethylenically unsaturatedmonomer different from ethylene and propylene is block-copolymerized orgraft-copolymerized.
 15. The process for producing a nonwoven polyesterstaple fiber fabric as claimed in claim 13, wherein the matrix polyesterpolymer is selected from polyalkylene terephthalates and polyalkyleneterephthalate-isophthalate copolymers.
 16. The process for producing anonwoven polyester staple fiber fabric as claimed in any one of claims13 to 15, wherein the polyester staple fibers have a degree ofcrystallization of 20% or less or a birefringence of 0.05 or less. 17.The process for producing a nonwoven polyester staple fiber fabric asclaimed in any one of claims 13 to 15, wherein the polyester staplefibers have a concentric or eccentric core-in-sheath conjugatestructures in which the sheath section is formed from the polymericblend, and core section is formed from a member selected from polyestersand polyamides.
 18. The process for producing a nonwoven polyesterstaple fiber fabric as claimed in any one of claims 13 to 15, whereinthe polyester staple fibers have a fiber length of 2 to 30 mm, andcrimps in a number of crimp of 3 to 13 crimps/25 mm and a percentage ofcrimp of 3 to 15%.
 19. The process for producing a nonwoven polyesterstaple fiber fabric as claimed in any one of claims 13 to 15, whereinthe nonwoven fabric has a percentage of non-opened fibers of 5% or less.20. The process for producing a nonwoven polyester staple fiber fabricas claimed in any one of claims 13 to 15, wherein the nonwoven fabrichas a bending resistance of 70 mm or less, as determined by thecantilever method.